Synthesis and luminescence properties of Ba3Lu(PO4)3:Sm3+ phosphor for white light-emitting diodes

Zaifa Yang; Denghui Xu; Jiayue Sun

doi:10.1364/OE.25.00A391

1. Introduction

In recent years, white light-emitting diodes (w-LEDs) have attracted increasing attentions from engineers and scientists in the solid-state luminescence field owing to the merits of being environmentally friendly, their long lifetime, energy-saving qualities, and high luminous efficiency [1–3]. At present, the most common method is to employ the yellow-emitting YAG:Ce³⁺ phosphor with blue InGaN chips to produce the practical white light emission [4]. However, commercial w-LED lamps are deficient in the red region, resulting in a lowly satisfactory color-rendering index and poor light performance. A suitable red-emitting phosphor for near ultraviolet (NUV) phosphor converted LEDs should have many potential applications, due to their excellent color rendering index, high color tolerance and high conversion efficiency into visible light [5]. Therefore, it is urgent to find new red phosphors that can be excited by NUV-LED chips for the fabrication of w-LEDs.

Phosphors based on a phosphate host is one of the most important luminescent materials and rare earth doped phosphates usually have excellent thermal stability, ideal charge stabilization and low sintering temperature, which have attracted more and more attention [6]. To our knowledge, eulytite-type orthophosphate with the general formula A^II₃M^III(PO₄)₃ (A = alkaline earth or Pb; M = trivalent rare earth, Bi, or V) have been reported [7–10]. The results show that eulytite-type orthophosphate are considered as suitable host matrices for phosphors due to the characteristics of high physical and chemical stability, water-resistant property, stable crystal structure, and excellent optical properties.

Owing to the great requirement for the red phosphors used in developing solid state lighting, such as LEDs, many different types of hosts have been developed, such as K₂TiF₆:Mn⁴⁺, MZnOS:Mn²⁺ (M = Ca, Ba), CuInS, BaNb₂O₆:Sm³⁺ and so on [11–14]. Among them, Sm³⁺ doped red phosphors played an important role in these fields. As is known, Sm³⁺ ion is an important activator for its narrow emission band and high quantum efficiency. The emission and excitation of Sm³⁺ belong to the 4f-4f transition, besides it has good red light emission excited by NUV light, thus causing extensive researches [15]. To the best of our knowledge, no paper has been published on the preparation of Sm³⁺ doped Ba₃Lu(PO₄)₃ phosphor. So we synthesized Ba₃Lu(PO₄)₃:Sm³⁺ phosphor via the high temperature solid-state reaction method. The high temperature solid-state reaction method is very important in the preparation of fluorescent materials. This method is not only used early but also widely used in real life. The samples prepared via high temperature solid-state reaction method has some outstanding features compared to other methods such as high brightness, low cost, simple preparation process and good quality powder. And the most important is that this method is easy to realize industrialized production [16].The luminescence properties of this phosphor were studied by photoluminescence excitation (PLE) spectrum, photoluminescence emission (PL) spectrum, concentration quenching, and decay curve analyses.

2. Experimental

The stoichiometric amounts of raw materials, BaCO₃ (A.R.), Lu₂O₃ (A.R.), (NH₄)₂HPO₄ (A.R.) and Sm₂O₃ (99.99%) were thoroughly mixed and ground in an agate mortar. After the stoichiometric amounts of the starting materials were mixed thoroughly, the mixtures were fired in a muffle furnace at 650 °C for 5 h, reground, and finally fired at 1250 °C for 3 h in air. After calcining, the samples were cooled to room temperature and ground thoroughly into powder for measurement.

The phase structure of the as-prepared phosphor was recorded by an X-ray Powder diffraction spectroscopy (XRD, Bruker D2, Karlsruhe, Germany) with Cu Kα radiation (λ = 1.5406 Å) operated at 30 kV tube voltage and 10 mA tube current. The morphology of the samples was determined by using a field-emission scanning electron microscope equipped with an energy-dispersive spectrometer (FE-SEM, S-4800, Hitachi, Japan). The amounts of Sm elements in precursor solution and filtrate were analyzed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) using a Perkin Elmer Optima 8000 instrument. The PL and PLE spectra of the samples were measured on a fluorescence spectrophotometer (F-7000, Hitachi, Japan) with a photomultiplier tube operating at 400 V, and 150 W Xe lamp used as an excitation source. Diffuse reflection spectra were recorded using a UV–Vis–NIR spectrophotometer (UV-3700, SHIMADZU) and white BaSO₄ powder was used as a reference standard. The luminescence decay curve was obtained using a spectrofluorometer (HORIBA, JOBIN YVON FL3-21), and the 370 nm pulse laser radiation was used as the excitation source. The temperature-dependence luminescence properties were measured on the same spectrophotometer, which was combined with a self-made heating attachment and a computer-controlled electric furnace (Tianjin Orient KOJI Co. Ltd, TAP-02).

3. Results and discussion

3.1 Structural studies

The structure of Ba₃Lu(PO₄)₃ compound is illustrated in Fig. 1(a). Ba₃Lu(PO₄)₃ reportedly crystallizes to a cubic crystal structure with a space group of I-43d (no.220) and lattice parameter values of a = 10.4760 Å, and V = 1149.71 Å³ [17,18]. As shown in Fig. 1(b), in this structure, the Ba²⁺/Lu³⁺ pairs of cations are disordered on a single crystallographic site, whereas the oxygen atoms disordered over two orientations (O1 and O2 with 35% and 65% occupancy factors, respectively) of the phosphate groups are distributed over three partially occupied sites [19]. As is known, the ionic radii of Lu³⁺ (r = 0.085 nm with CN = 9) and Sm³⁺ (r = 0.098 nm with CN = 9) are very close [20]. Given the identical electric charges of Lu³⁺ and Sm³⁺ and their similar radii, doped Sm³⁺ ions can substitute for Lu³⁺ sites.

Fig. 1 (a) Structural view of Ba₃Lu(PO₄)₃; (b) The coordination environment of Ba²⁺/Lu³⁺ site.

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A SEM is a powerful magnification tool that utilizes focused beams of electrons to obtain information. The high-resolution, 3D images produced by SEM provide topographical, morphological and compositional information, which makes them invaluable in a variety of science and industry applications [21]. Figure 2(a) and Fig. 2(b) shows the surface morphology of Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor at different magnifications. From the SEM images it is observed that the morphology of the powders is basically flaky polycrystalline constituted by microcrystalline agglomerated particles. In the current study, the SEM images of the phosphor reveal the average particle sizes of 2–10 μm. This is a suitable size for fabrication of solid-state lighting devices.

Fig. 2 SEM images of Ba₃Lu(PO₄)₃:0.05Sm³⁺ sample under different magnification (a): 2.2 k × ; (b) 3.5 k × .

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A series of XRD patterns of Ba₃Lu(PO₄)₃:Sm³⁺ phosphors with different doping contents as well as the Joint Committee for Powder Diffraction Standard (JCPDS) file 43-0212 [Ba₃Lu(PO₄)₃] are illustrated in Fig. 3. It can be seen that no detectable impurity phase is observed in the obtained samples when the doping contents is below 0.09, indicating that a single-phase phosphor is obtained and the doped Sm³⁺ ions do not change the host crystal lattice. In the meantime, the diffraction peaks shift to smaller angles with increasing Sm³⁺ content owing to the different ionic radii between Sm³⁺ and Lu³⁺, indicating that Sm³⁺ ions have been doped into the crystal lattices of the cubic instead of forming the impurity phase. In addition, the Miller indices of Ba₃Lu(PO₄)₃:Sm³⁺ phosphors were calculated by using equation reported by Tamrakar et al. and given in Table 1 [22]. In order to prove that the actual Sm³⁺ content corresponds to a nominal composition, the hydrothermal supernatant (30 ml) was measured by inductively coupled high frequency plasma atomic emission spectroscopy (ICP-AES) to detect the residual content of Sm³⁺ in solution (see Table 2).

Fig. 3 XRD patterns of Ba₃Lu(PO₄)₃:Sm³⁺ with different Sm³⁺ contents. The standard data for Ba₃Lu(PO₄)₃ (JCPDS card no. 43-0212) is shown as a reference.

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Table 1. Miller indices value Ba₃Lu(PO₄)₃:Sm³⁺ phosphor

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Table 2. The doping rate of Sm³⁺ in the Ba₃Lu(PO₄)₃:x% Sm³⁺ (x = 1, 3, 5)

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3.2 Excitation and emission spectra

To record the luminescence spectra for the prepared phosphor and the possibility for application in w-LEDs, it is necessary to know the excitation wavelengths of Sm³⁺. For this purpose, we measured the excitation spectrum of Ba₃Lu(PO₄)₃:Sm³⁺ with different Sm³⁺ contents from 250 to 550 nm monitored at 600 nm. As is shown in Fig. 4(a), it is easy to see there are several excitation peaks of Sm³⁺, which are located in the wavelength range of 325–500 nm, assigning to the forbidden f-f transition of Sm³⁺, ⁶H_5/2→⁴K_17/2 (343 nm), ⁶H_5/2→⁴H_7/2 (360 nm), ⁶H_5/2→⁶P_7/2(373 nm), ⁶H_5/2→⁴F_7/2 (403 nm), ⁶H_5/2→⁴G_9/2 (438 nm), ⁶H_5/2→⁴I_11/2 (473 nm) [23, 24]. From the perspective of excitation spectrum, the intensity of transition at 403 nm is higher than any other transitions. This result also indicates that the obtained phosphor can be efficiently excited by NUV chips and will be a potential candidate as light-conversion phosphor for w-LEDs.

Fig. 4 (a) Excitation spectra of Ba₃Lu(PO₄)₃:Sm³⁺ with different Sm³⁺ contents; (b) The diffuse reflectance spectra of Ba₃Lu(PO₄)₃ host, Ba₃Lu(PO₄)₃:0.03Sm³⁺ and Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphors.

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The reflectance spectra of Ba₃Lu(PO₄)₃ host, Ba₃Lu(PO₄)₃:0.03Sm³⁺, Ba₃Lu(PO₄)₃: 0.05Sm³⁺ phosphors are shown in Fig. 4(b). The spectra shows a strong absorption band in the wavelength ranging from 400 to 800 nm, and then shows a remarkable drop from 200 to 350 nm that corresponds to the band transition in the Ba₃Lu(PO₄)₃ host lattice. When Sm³⁺ ions is introduced into the host lattices, several weak absorption bands in the larger wavelength range 340–500 nm are observed. The absorption range from 200 to 500 nm in the Ba₃Lu(PO₄)₃:Sm³⁺ phosphor matched well with the photoluminescence excitation spectrum in Fig. 4(a).

The emission spectra of Ba₃Lu(PO₄)₃:xSm³⁺ (x = 0.01, 0.03, 0.05,0.07 and 0.09) phosphors measured at λ_ex = 403 nm (⁶H_5/2→⁴F_7/2) excitation wavelength are shown in Fig. 4(a). Three emission peaks were observed at 564, 600 and 647 nm corresponding to ⁴G_5/2→⁶H_5/2, 4G_5/2→⁶H_7/2, and ⁴G_5/2→⁶H_9/2, respectively. The emission peak centered at 564 nm (⁴G_5/2→6H_5/2) is originated due to purely magnetic dipole moment, second peak at 647 nm (⁴G_5/2→⁶H_9/2) is due to purely electric dipole moment and the other at 600 nm (⁴G_5/2→⁶H_7/2) is due to both magnetic and electric dipole moments [25, 26]. Generally, the intensity ratio of electric dipole to magnetic dipole transitions is useful to understand the symmetry of local environment around the trivalent ⁴f₅ ions. In the present phosphor, the magnetic dipole transition is more intense than electric dipole transition suggested that there is no deviation from inversion center and more symmetric in nature [27, 28]. It is observed from Fig. 5(a) that there is no change in the position of emission band for all doping concentrations. However, the emission intensity changes with doping concentration of Sm³⁺ ions. It is observed the emission intensity of the sample firstly increases with the concentration of Sm³⁺ increasing. This is because the distance between two adjacent Sm³⁺ ions is decreased by increasing Sm³⁺ concentration, and the interaction between Sm³⁺-Sm³⁺ ions is enhanced, which causes the nonradiative energy transfer between two Sm³⁺ ions. The electric multipolar interaction and exchange interaction are involved in the energy transfer [29]. Initially, the emission reaches to a maximum at x = 0.05 (critical concentration), beyond that the emission intensity begins to decrease with increase in concentration due to concentration quenching effect.

Fig. 5 (a) Emission spectra of Ba₃Lu(PO₄)₃:Sm³⁺ with different Sm³⁺ contents; (b) The relationship of lg(x) versus lg(I/x) for Ba₃Lu(PO₄)₃:xSm³⁺ (x = 0.05, 0.07, 0.09) phosphor.

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In general, the concentration quenching is mainly caused by non-radiative energy transfer processes (cross-relaxation) among Sm³⁺ ions, which occurs as a result of an exchange interaction or a multipole–multipole interaction [30]. In order to identify the type of interaction mechanism, it is necessary to obtain the critical distance (R_c) that is the critical separation between the donor (activator) and acceptor (quenching site). According to the theory of Blasse, the critical transfer distance (R_c) of energy transfer can be calculated by the critical concentration of the activator ion [31]:

R_{c} \approx 2 {[\frac{3 V}{4 π X_{c} N}]}^{1 / 3}

where V is the volume of one unit cell, N is the number of the cationic sites occupied by activators in one unit cell, and Xc is the critical concentration of the activator ion. For Ba₃Lu(PO₄)₃ host, V = 1149.71 Å³, N = 4 and X_c = 0.05. Therefore, by using Eq. (1), the R_c value of Sm³⁺ can be quickly obtained to be 22.23 Å. According to theory of Van Uitert, if the critical distance between the sensitizer and activator is shorter than 5 Å, the energy transfers type is exchange interaction [32]. The above calculation result suggests that the energy transfer among Sm³⁺ ions in Ba₃Lu(PO₄)₃:Sm³⁺ phosphor does not occur in this case. According to Van Uitert, if energy transfer occurs among the same type of activators, the intensity of the multipolar interaction can be determined from the change in the emission intensity from the emitting level that has the multipolar interaction. The emission intensity (I) per activator ion can be expressed as [33]:

\frac{I}{x} = K {(1 + β {(x)}^{Q / 3})}^{- 1}

where I is the emission intensity, x is the concentration of the activator ions above the concentration quenching point, β and K are constants for the same conditions, and Q is the function of multipole–multipole interaction for 6 (dipole–dipole), 8 (dipole–quadrupole) or 10 (quadrupole–quadrupole). As shown in Fig. 5(b), to obtain a correct Q the dependence of log(I/x) on log(x) is plotted, and it yields a straight line with a slope of -Q/3. The fitting result for Sm³⁺ emission centers, which is corresponding to the high Sm³⁺ concentration Ba₃Lu(PO₄)₃:xSm³⁺ phosphor compositions, is shown in Fig. 5(b). Based on the fitting results, the slope is −1.66, and the value of Q can be calculated as 4.98, which is approximately equal to 6. This indicates that the dipole–dipole interaction is the major mechanism for concentration quenching in Ba₃Lu(PO₄)₃: Sm³⁺ phosphor.

3.3 Decay curve and quantum efficiency

For Ba₃Lu(PO₄)₃:xSm³⁺ phosphors with different concentrations (x = 0.01,0.03, 0.05, 0.07and 0.09), the decay of emission intensity at 600 nm as a function of time is depicted in Fig. 6. The decay curve for ⁴G_5/2→⁶H_7/2 transition of Sm³⁺ can be expressed by a double exponential equation as follows [34]:

I (t) = A_{1} \exp (- t / t_{1}) + A_{2} \exp (- t / t_{2})

where I is the luminescence intensity at time t, A₁ and A₂ are constants, t is the time, and t₁ and t₂ are the decay time for the exponential components. Then, the average decay lifetime can be calculated as follows:

Fig. 6 Decay curves of Ba3Lu(PO4)3:xSm3 + at different concentrations (λ_ex = 370 nm and λ_em = 600 nm).

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τ = \frac{A_{1} t_{1}^{2} + A_{2} t_{2}^{2}}{A_{1} t_{1} + A_{2} t_{2}}

According to the Eq. (4), the average lifetimes of Sm³⁺ ions calculated using the decay profiles are 2.32, 2.19, 1.78, 1.61, and 1.46 ms for Ba₃Lu(PO₄)₃:xSm³⁺ with x = 0.01, 0.03, 0.05, 0.07 and 0.09, respectively. The lifetime decreases with increased concentration. These results show that the lifetime is short enough for potential applications in displays and lights.

In general, for the practical application of phosphors for LEDs, the quantum efficiency of the phosphor is an important factor to be considered. We have also recorded the quantum yield of Ba₃Lu(PO₄)₃:xSm³⁺ phosphors. The quantum efficiency can be described by the following equation [35]:

η_{Q E} = \frac{\int λ P (λ) d λ}{\int λ [E (λ) - R (λ)] d λ}

where P(λ), E(λ) and R(λ) are the intensities per unit wavelength in the emission, excitation and reflection spectra of the Ba₃Lu(PO₄)₃:xSm³⁺ phosphor, respectively. Under the excitation of 403 nm, the recorded quantum yield values of Ba₃Lu(PO₄)₃:xSm³⁺ are 0.14, 0.31, 0.48, 0.24, and 0.19 for x = 0.01, 0.03, 0.05, 0.07, and 0.09 respectively, which are consistent with the variation of the emission intensities.

3.4 CIE coordinates and thermal properties

Thermal stability is an important technological parameter for phosphors used in solid-state lighting, since it exerts significant influence on the light output as well as color-rendering index. The temperature-dependent emission spectra of the Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor measured at 25 °C–300 °C under 403 nm excitation were shown in Fig. 7(a). One can see that the intensity of emission spectrum gradually decreases with the increase of temperature due to the thermal quenching effect. As shown in Fig. 7(b), when the measurement temperature is up to 250 °C, the emission intensities of ⁴F_9/2→⁶H_13/2 decrease to 84.6% of the initial emission intensities measured at 25 °C, which is higher than that of Y₃Al₅O₁₂:Ce³⁺ commercial phosphor (58%) [36].

Fig. 7 (a) Temperature dependence of the PL intensity of Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor; (b) The relative emission intensity of Ba₃Lu(PO₄)₃:0.05Sm³⁺ and YAG:Ce as a function of temperature; (c) Activation energy for thermal quenching of Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor.

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To further investigate the thermal quenching phenomenon and obtain the activation energy for thermal quenching, the activation energy from the thermal quenching can be calculated using the Arrhenius equation [37]:

I (T) = \frac{I_{o}}{1 + c \exp (- (Δ E / K T))}

where I₀ is the initial intensity, I_(T) is the intensity at a given temperature T, ΔE is the activation energy for thermal quenching, c is a constant for a certain host, and K is the Boltzmann constant (8.629 × 10⁻⁵ eV). Therefore, we used the Eq. (6) to fit the temperature dependent luminescent intensities shown in Fig. 7(b). During the fitting process, the activation energy (ΔE) was deduced to be 0.142 eV. This result indicates that the as-prepared phosphors possess good thermal stability properties.

Color coordinate is also one of the important factors for evaluating phosphors’ performance. The Commission Internationale de L’Eclairage (CIE) chromaticity diagram of the prepared Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor is shown in Fig. 8(a). The color coordinate for Ba₃Lu(PO₄)₃:0.05Sm³⁺ under 403 nm excitation is shown as (0.602, 0.389), which means that the emitted light is in the region of orange reddish light. In order to investigate the possibility of the as-synthesized phosphor in application for NUV LED, a prototype red LED was fabricated by pre-coating Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor onto a 404 nm emitting InGaN chip. The emission spectra of the original 404 nm emitting InGaN chip and prototype red LED under 20 mA forward bias current are shown in Fig. 8(b). The band at 404 nm results from emission of InGaN chip. When coated with Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor, the near UV light was absorbed by the phosphor, and simultaneously down-converted into an intensive red light. The results demonstrated that Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor could efficiently absorb the NUV light, thereby making it a good candidate as red component of NUV LED application.

Fig. 8 (a) The emission spectra of red pc-LED (Inset: photo of red LED under a bias current of 20 mA); (b) Chromaticity coordinates of Ba₃Lu(PO₄)₃:0.05Sm³⁺ phosphor in the CIE 1931 chromaticity diagram.

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4. Conclusions

In summary, the novel phosphor of Ba₃Lu(PO₄)₃ doped with rare earth ions of Sm³⁺ were synthesized by a solid-state reaction. The PLE spectra shows that the phosphor can be efficiently excited by ultraviolet light and emit a satisfactory orange-red performance, nicely, fitting in well with the widely used NUV LED chip. The thermal stability of Ba₃Lu(PO₄)₃:0.05Sm³⁺ sample is superior to the commercial YAG:Ce³⁺ phosphor. All the obtained results indicate that these phosphors might be a promising reddish-orange emitting phosphor used in w-LEDs.

Funding

National Natural Science Foundation of China (NSFC) (21576002).

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Peak #	2θ	θ	sin²θ	sin²θ/ sin²θ_min	*(sin²θ/ sin²θ_min)3**	h² + k² + l²	hkl
1	20.812	10.406	0.0326	1	3	6	(211)
2	24.057	12.029	0.0434	1.3313	3.9939	8	(220)
3	26.951	13.476	0.0543	1.6656	4.9968	10	(310)
4	32.005	16.003	0.0760	2.3313	6.9939	14	(321)
5	40.418	20.209	0.1193	3.6595	10.9785	22	(332)
6	42.295	21.147	0.1301	3.9908	11.9724	24	(422)
7	44.106	22.053	0.1410	4.3251	12.9755	26	(510)
8	47.584	23.792	0.1627	4.9908	14.9724	30	(521)
9	54.001	27	0.2061	6.3221	18.9663	38	(611)
10	55.535	27.768	0.2171	6.6595	19.9785	40	(620)
11	57.018	28.509	0.2278	6.9877	20.9632	42	(541)
12	61.354	30.677	0.2603	7.9847	23.9540	48	(444)
13	65.521	32.76	0.2928	8.9816	26.9448	54	(721)
14	66.861	33.43	0.3035	9.3098	27.9294	56	(642)
15	78.618	39.309	0.4013	12.3098	36.9294	74	(831)

Sample	Nominal doping concentration of Eu-ion (mole percent)	Doping quality of Eu-ion (μg)	Residual concentration of Eu-ion (μg/ml)	Real doping rate of Eu-ion (percent)	Real doping concentration of Eu-ion (mole percent)
1	1%	1504	0.00 (<0.01)	100% (>99.80%)	0.9998%
2	3%	4512	0.00 (<0.01)	100% (>99.96%)	2.9969%
3	5%	7520	0.00 (<0.01)	100% (>99.98%)	4.9988%

Peak #	2θ	θ	sin²θ	sin²θ/ sin²θ_min	*(sin²θ/ sin²θ_min)3**	h² + k² + l²	hkl
1	20.812	10.406	0.0326	1	3	6	(211)
2	24.057	12.029	0.0434	1.3313	3.9939	8	(220)
3	26.951	13.476	0.0543	1.6656	4.9968	10	(310)
4	32.005	16.003	0.0760	2.3313	6.9939	14	(321)
5	40.418	20.209	0.1193	3.6595	10.9785	22	(332)
6	42.295	21.147	0.1301	3.9908	11.9724	24	(422)
7	44.106	22.053	0.1410	4.3251	12.9755	26	(510)
8	47.584	23.792	0.1627	4.9908	14.9724	30	(521)
9	54.001	27	0.2061	6.3221	18.9663	38	(611)
10	55.535	27.768	0.2171	6.6595	19.9785	40	(620)
11	57.018	28.509	0.2278	6.9877	20.9632	42	(541)
12	61.354	30.677	0.2603	7.9847	23.9540	48	(444)
13	65.521	32.76	0.2928	8.9816	26.9448	54	(721)
14	66.861	33.43	0.3035	9.3098	27.9294	56	(642)
15	78.618	39.309	0.4013	12.3098	36.9294	74	(831)

Sample	Nominal doping concentration of Eu-ion (mole percent)	Doping quality of Eu-ion (μg)	Residual concentration of Eu-ion (μg/ml)	Real doping rate of Eu-ion (percent)	Real doping concentration of Eu-ion (mole percent)
1	1%	1504	0.00 (<0.01)	100% (>99.80%)	0.9998%
2	3%	4512	0.00 (<0.01)	100% (>99.96%)	2.9969%
3	5%	7520	0.00 (<0.01)	100% (>99.98%)	4.9988%

Synthesis and luminescence properties of Ba₃Lu(PO₄)₃:Sm³⁺ phosphor for white light-emitting diodes

Abstract

1. Introduction

2. Experimental

3. Results and discussion

3.1 Structural studies

3.2 Excitation and emission spectra

3.3 Decay curve and quantum efficiency

3.4 CIE coordinates and thermal properties

4. Conclusions

Funding

References and links

Cited By

Figures (8)

Tables (2)

Equations (6)

Optics Express